Adhesive-backed articles

ABSTRACT

Methods of preparing adhesive-backed articles and methods of applying adhesives backed articles are described. The adhesive-backed articles include a compliant film and a pressure-sensitive adhesive having a microstructured surface opposite the compliant film.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/357,151 filed Feb. 3, 2003, now pending, which is acontinuation-in-part of U.S. patent application Ser. No. 09/311,101,filed May 13, 1999, now issued as U.S. Pat. No. 6,524,675 on Feb. 25,2003.

FIELD OF THE INVENTION

The present invention relates to an adhesive-backed article, moreparticularly to such an adhesive-backed article having an adhesive witha microstructured surface bonded to a compliant film, and even moreparticularly to channels, with a specific volume per unit area, formedby the microstructured surface in the adhesive which permit thedesirable properties of positionability and fluid egress to a peripheryof the article without adversely affecting the surface appearance of thefilm after application onto a substrate.

BACKGROUND OF THE INVENTION

Films are often bonded to substrates utilizing pressure-sensitiveadhesives. The films are generally bonded to a variety of differentsubstrates including, for example, surfaces on motor vehicles. Theinterface between the adhesive and the contact surface of the substrateis important to the performance of the film. The interface between theadhesive and the substrate is affected by several factors. For example,the application may be affected by the type of adhesive used, the sizeand type of the films utilized, the surface of the substrate upon whichthe article is applied, the application technique utilized, orcombinations thereof.

Adhesive-backed films are often used for decorative purposes. Theplacement of a film into a specific position prior to the formation of abond between the adhesive and the substrate is often difficult, butimportant for aesthetic reasons. Some adhesive-backed articles areunable to slide on the surface of the substrate and will adhere with theslightest contact on the surface of the substrate. Such articles canoften be particularly difficult to reapply if they inadvertently adhereto the substrate. The inability to slide the adhesive-backed article inplace can adversely affect the positioning of the article or causedamage to the article upon attempted repositioning after adhesion.

The decorative articles also require that the adhesive-backed article beable to evacuate air or other fluids trapped underneath the adhesiveduring the bonding step. The ability to bleed fluids and eliminatebubbles from underneath the article improves the overall appearance ofthe article. Additionally, bubbles under a film can adversely affect theadhesive performance of the article.

Thin films are often utilized on surfaces so that the adhesive filmblends with the substrate upon which the film is applied. Additionally,thinner films are generally more flexible and therefore suited forapplication on contoured surfaces. However, the utilization of thinfilms can create an appearance problem. The thinner films have atendency to show all surface abnormalities or uneven portions of eitherthe adhesive or the substrate upon which the adhesive-backed article isapplied.

SUMMARY OF THE INVENTION

The present invention relates to an adhesive-backed article. The articleincludes a compliant film with a pressure sensitive adhesive bonded to alower surface of the film. The pressure sensitive adhesive includes amicrostructured surface opposite the compliant film.

In accordance with the present invention, the microstructured surfacedefines channels in the pressure sensitive adhesive. The channelscomprise a volume of at least 1×10³ μm³ per any 500 μm diameter circulararea in the adhesive. The channels are utilized to create exit pathwaysfor fluid egress to a periphery of the article when the article isapplied to a substrate. The adhesive-backed article sufficiently bondsto a substrate as indicated by a wet out value of at least 85%. Thechannels are substantially undetectable on an upper surface after finalapplication of the article onto a substrate.

In general, the adhesive-backed article of the present invention ispositionable over a substrate prior to forceful application of thearticle onto the substrate. The microstructured surface of the adhesivepermits the article to either slide over the surface of a substrate, orbe easily removed from the surface of the substrate, until enoughpressure is applied to enable a bond between the adhesive and thesurface of the substrate. The article of the present invention alsoenhances the egress of fluid from the interface between the adhesive andthe substrate as a bonding force is applied to the article. Themicrostructured features are particularly suited for applicationsutilizing thin films, ie less than 300 μm.

The channels of the present invention can take various shapes orpatterns. The channels are generally formed by structures in theadhesive that create the microstructured surface. The structures may beeither placed randomly about the surface of the adhesive or placed inregular patterns.

The microstructured surface can be formed by directly embossing thepressure sensitive adhesive layer with the structures. Alternatively, aliner or backing can be embossed first and then coated with a pressuresensitive adhesive to impart the structures to the adhesive. The film istypically laminated or bonded to a side of the adhesive layer oppositethe microstructured features.

It is an advantage to provide an adhesive-backed article that haspathways in the adhesive for fluid egress and permits positioning of thearticle without adversely affecting the appearance of the article. Thechannels define pathways to the periphery of the article that permit theflow of fluid trapped between the adhesive and the surface of thesubstrate. Additionally, the microstructured surface of the presentinvention enable the positioning of the article onto a substrate.Further, the microstructured adhesive does not result in observableperiodic patterns on the exposed surface of the film after applicationof the article onto a substrate.

For purposes of the present invention, the following terms used in thisapplication are defined as follows:

-   -   “microscopic” refers to structures of small enough dimension so        as to require an optic aid to the naked eye when viewed from any        plane of view to determine its shape. One criterion is found in        Modern Optic Engineering by W. J. Smith, McGraw-Hill, 1966,        pages 104-105 whereby visual acuity, “ . . . is defined and        measured in terms of the angular size of the smallest character        that can be recognized.” Normal visual acuity is considered to        be when the smallest recognizable letter subtends an angular        height of 5 minutes of arc on the retina. At typical working        distance of 250 mm (10 inches), this yields a lateral dimension        of 0.36 mm (0.0145 inch) for this object;    -   “microstructure” means the configuration of structures wherein        at least 2 dimensions of the structures are microscopic. The        topical and/or cross-sectional view of the structures must be        microscopic.;    -   “embossable” refers to the ability of a pressure-sensitive        adhesive layer or liner to have part of its surface raised in        relief, especially by mechanical means;    -   “wetting” or “wet out” means spreading out over and intimately        contacting a surface;    -   “positionable” or “positionability” refers to those        adhesive-backed articles that can easily slide over a substrate        without grabbing or bonding to the substrate absent the        application of a force, or adhesive-backed articles that upon        light force are capable of releasably bonding to a substrate and        upon removal retain at least some form of the original        microstructured surface;    -   “release liner”, used interchangeably with the term “liner”,        refers to a flexible sheet which after being placed in intimate        contact with pressure-sensitive adhesive surface may be        subsequently removed without damaging the adhesive coating;    -   “microstructured liner” refers to a liner with at least one        microstructured surface, which is suitable for contact with an        adhesive;    -   “backing” refers to a thin, flexible sheet which, after being        placed in intimate contact with pressure-sensitive adhesive can        not be subsequently removed without damaging the adhesive        coating;    -   “microstructured backing” refers to a backing with a        microstructured surface.    -   “substrate” refers to a surface to which the pressure-sensitive        adhesive coating is applied for an intended purpose;    -   “tape” refers to a pressure-sensitive adhesive coating applied        to a backing.    -   “inelastic deformation” means the permanent set at a given        strain resulting from a film being stretched to 15% under        tension and dissipating that tension.    -   “compliant” refers to a polymeric film that is soft and flexible        as well as having sufficient inelastic deformation after being        stretched so that once stretched, the film does not recover to        its original length;    -   “bleedability” or “air-bleedability” refers to the egress of        fluids, particularly air, from the interface between the        adhesive and the surface of the substrate; and    -   “appearance” means the visual characteristics of the article as        viewed from the exposed surface of the film after application of        the article onto a substrate.

BRIED DESCRIPTION OF THE DRAWINGS

The invention will be more fully appreciated with reference to thefollowing drawings in which similar reference numerals designate like oranalogous components throughout and in which:

FIG. 1 is an enlarged, fragmentary, cross-sectional view of anadhesive-backed article according to the invention;

FIG. 2 a is a segmented planar view of a microstructured adhesivesurface according to the present invention;

FIG. 2 b is a segmented view of the adhesive backed article highlightingthe microstructured features of the present invention;

FIG. 3 a is a perspective view of one embodiment of a microstructuredfeature according to the present invention;

FIG. 3 b is a perspective view of one embodiment of a truncatedmicrostructured feature according to the present invention;

FIG. 4 a is a perspective view of one embodiment showing a doublefeatured microstructured element according to the present invention;

FIG. 4 b is a perspective view of another embodiment showing a doublefeatured microstructured element according to the present invention;

FIG. 5 is a sectional view showing the configuration of amicrostructured surface of an adhesive layer;

FIG. 6 is a sectional view showing a second configuration ofmicrostructured surface of an adhesive layer;

FIG. 7 is a sectional view showing an additional configuration of amicrostructured surface of an adhesive layer;

FIG. 8 is a perspective view of a release liner suitable for forming amicrostructured surface in an adhesive according to the presentinvention;

FIG. 9 is a graph indicating the surface roughness of the article of thepresent invention after it is applied onto a substrate; and

FIG. 10 is a graph indicating the surface roughness of a comparativearticle after it is applied onto a substrate.

DETAILED DESCRIPTION

The present inventive article 10, as depicted in FIG. 1, includes acompliant film 12 having an opposing surfaces 14, 16. A pressuresensitive adhesive 18 is bonded to surface 16 of the compliant film 12.The pressure sensitive adhesive 18 includes a surface 20 that can bebonded to a substrate (not shown). The pressure sensitive adhesive 18includes structures 22 which define channels 24. A release liner 26 isreleasably attached to the pressure sensitive adhesive 18. The releaseliner 26 includes protrusions 28 that are utilized to form correspondingchannels 24 and structures 22 in the pressure sensitive adhesive 18. Therelease liner 26, shown in a partially removed state, is fullydetachable and is used to protect the pressure sensitive adhesive priorto application of the article 10 on a substrate.

The article of the present invention is an improvement over structuredadhesives that provide some degree of egress for entrapped air. However,certain structured adhesives are not easily positioned on a substrate.Further, the structures often show through the outer surface of the filmafter forceful application of the article onto the substrate. This isparticularly true with thin films that tend to highlight any underlyingsurface differences. The present invention imparts a microstructuredsurface which defines channels in a pressure sensitive adhesive withspecific rheological characteristics to address the issues associatedwith conventional adhesive-backed articles. The channels in the adhesiveof the present invention have specific dimensions and characteristics toimprove the positionability and fluid egress to a periphery of thearticle. Additionally, the characteristics of the channels render themicrostructured surface of the adhesive substantially undetectable tothe human eye when viewed from the exposed surface of the article afterapplication.

The compliant film utilized in the present inventive article isgenerally made of various plastic materials used conventionally by thoseskilled in the art. Suitable films include, for example, vinyl,polyvinyl chloride, plasticized polyvinyl chloride, polyurethane,polyethylene, polypropylene, fluororesin or the like. The thickness filmcan vary widely according to a desired application, but is usuallywithin a range from about 300 μm or less, and preferably about 25 μm toabout 100 μm.

A specific example of a suitable compliant layer is a plasticizedpolyvinyl chloride film, and has sufficient inelastic deformation afterbeing stretched so that when stretched, the film does not recover to itsoriginal length. Preferably, the film has an inelastic deformation of atleast 5% after being stretched once to 115% of their original length. Atypical formulation of the vinyl film includes polyvinyl chloride resin,light and/or heat stabilizer(s), plasticizer, and optionally, pigment.The amount of plasticizer is generally less than about 40% by weight,and is preferably composed of polymeric non-migratable plasticizerswhich are compatible with the vinyl film and provide the necessaryflexibility and durability. A suitable plasticizer is a combination ofpolymeric polyester elastomer and an ethylene vinyl acetate copolymer(such as Elvaloy 742 made by DuPont Co.) soluable in aromatic solventsand present in amounts of about 26 parts and 10 parts, respectively, per100 parts vinyl resin.

Primers may optionally be used to enhance the bond between the film andthe adhesive. The type of primer will vary with the type of film andadhesive used and one skilled in the art can select an appropriateprimer. Examples of suitable primers include chlorinated polyolefins,polyamides, and modified polymers disclosed in U.S. Pat. Nos. 5,677,376,5,623,010 and those disclosed in WO 98/15601 and WO 99/03907, and othermodified acrylic polymers. Typically, primers are dispersed into anadequate solvent in very low concentrations, e.g., less that about 5%solids, and coated onto the film, and dried at room or elevatedtemperatures to form a very thin layer. Typical solvents used mayinclude water, heptane, toluene, acetone, ethyl acetate, isopropanol,and the like, used alone or as blends thereof.

In accordance with the present invention, useful pressure sensitiveadhesives include those which are capable of retaining microstructuredfeatures on an exposed surface after being embossed with amicrostructured molding tool, backing or liner, or after being coated ona microstructured molding tool, backing or liner from which it issubsequently removed. The particular pressure sensitive adhesiveselected for a given application is dependent upon the type of substratethe article will be applied onto and the microstructuring methodemployed in producing the adhesive-backed article. Additionally, usefulmicrostructured pressure sensitive adhesives should be capable ofretaining their microstructured surfaces for a time sufficient to allowutilization of the adhesive-backed article.

Any pressure-sensitive adhesive is suitable for the invention. Adhesivesare typically selected based upon the type of substrate that they are tobe adhered to. Classes of pressure-sensitive adhesives include acrylics,tackified rubber, tackified synthetic rubber, ethylene vinyl acetate,silicone, and the like. Suitable acrylic adhesives are disclosed, forexample, in U.S. Pat. Nos. 3,239,478, 3,935,338, 5,169,727, RE 24,906,4,952,650, and 4,181,752. A preferred class of pressure-sensitiveadhesives are the reaction product of at least alkyl acrylate with atleast one reinforcing comonomer. Suitable alkyl acrylates are thosehaving a homopolymer glass transition temperature below about −10° C.and include, for example, n-butyl acrylate, 2-ethylhexylacrylate,isoctylacrylate, isononlyl acrylate, octadecyl acrylate and the like.Suitable reinforcing monomers are those having a homopolymer glasstransition temperature about −10° C., and include for example, acrylicacid, itaconic acid, isobornyl acrylate, N,N-dimethylacrylamide, N-vinylcaprolactam, N-vinyl pyrrolidone, and the like.

The adhesives may be polymers that are dispersed in solvent or water andcoated onto the release liner and dried, and optionally crosslinked. Ifa solventborne or waterborne pressure-sensitive adhesive composition isemployed, then the adhesive layer must undergo a drying step to removeall or a majority of the carrier liquid. Additional coating steps may benecessary to achieve a smooth surface. The adhesives may also be hotmelt coated onto the liner or microstructured backing. Additionally,monomeric pre-adhesive compositions can be coated onto the liner andpolymerized with an energy source such as heat, UV radiation, e-beamradiation.

The thickness of the adhesive is dependent upon several factors,including for example, the adhesive composition, the type of structuresused to form the microstructured surface, the type of substrate, and thethickness of the film. Those skilled in the art are capable of adjustingthe thickness to address specific application factors. In general, thethickness of the adhesive layer is greater than the height of thestructures which comprise the microstructured surface. Preferably, thethickness of the adhesive layer is within a range from about 10 to about50 μm.

The pressure sensitive adhesive can optionally include one or moreadditives. Depending on the method of polymerization, the coatingmethod, the end use, etc., additives selected from the group consistingof initiators, fillers, plasticizers, tackifiers, chain transfer agents,fibrous reinforcing agents, woven and non-woven fabrics, foaming agents,antioxidants, stabilizers, fire retardants, viscosity enhancing agents,coloring agents, and mixtures thereof can be used.

The pressure sensitive adhesive of the present invention includes amicrostructured surface on an exposed surface of the adhesive oppositethe compliant film. The microstructured surface defines channels in theadhesive. Channels are continuous open pathways or grooves that extendinto the adhesive from the exposed surface. The channels eitherterminate at the peripheral portion of the adhesive layer or communicatewith other channels that terminate at a peripheral portion of thearticle. Upon application of the article onto a substrate, the pathwaysprovide an egress to a periphery of the article for fluid trapped at theinterface between the adhesive and the substrate.

The channels are created to define a specific volume per any given areaof the microstructured surface of the adhesive. The minimum volume perunit area of the adhesive ensures adequate egress for fluids at theinterface of the substrate and the adhesive. Preferably, the channelsdefine a volume of at least 1×10³ μm³ per any 500 82 m diameter circulararea in a two-dimensional plane of the adhesive. Most preferably, thechannels define a volume in the range of above 1.0×10³ μm³ to about1×10^(7 μm) ³ on any 500 μm diameter circular area.

The channels of the present invention at least partially disappear uponfinal application of the article, in order to provide a desirableadhesion to the exposed surface of the film. The ability of the channelsto at least partially disappear is dependent upon the shape of thechannel and the rheology of the adhesive. In accordance with the presentinvention, the channel's size and dimensions are selected for thespecific pressure sensitive adhesive compositions to obtain a result ofat least 85% according to the percent wet out test discussed in the“Examples” section below. The proper wet out enables a sufficient sealbetween the article and the substrate.

The shape of the channels can vary widely according to the processingmethods, but each preferably has a V-shaped, U-shaped, rectangular ortrapezoidal cross section on observation in a transverse direction.FIGS. 2A and 2B show a segmented view of the inventive article 30highlighting trapezoidal channels 34 in the adhesive 38. Theadhesive-backed article 30 includes film 32 and adhesive 38. Thetrapezoidal channels 34 and corresponding structures 36 are formed inthe adhesive 38. Side walls 35 of the structures 36 define side wallsfor the channels 34.

The limits of dimensions of the channels can be described by use of theaspect ratio. The aspect ratio is defined as the ratio of the greatestmicroscopic dimension of the channel parallel to the plane of thecontinuous layer of adhesive to the greatest microscopic dimension ofthe channel perpendicular to the plane of the continuous layer ofadhesive. The aspect ratio is measured by taking the cross-sectionaldimensions of the channel at an angle perpendicular to the wall of thechannel. Depending on the specific type of channel, the limits of theaspect ratio would be about 0.1 to about 20. For example, the structuresof FIG. 7 would define channels that would have a preferred aspect ratioof about 10 to about 15.

Channels are generally created by embossing or forming a plurality ofstructures into the adhesive. The structures may be present in either arandom array or in regular patterns. Individual structures at leastpartially define a portion of a channel in the adhesive. Selectedpatterns could include rectilinear patterns, polar patterns and otherconventional regular patterns. A plurality of structures combine tocreate the continuous channels on the surface of the adhesive.

The shape of the structures formed in the pressure sensitive adhesive tocreate the microstructured surface can vary. Examples of structureshapes include but are not limited to those selected from the groupconsisting of hemispheres, prisms (such as square prisms, rectangularprisms, cylindrical prisms and other similar polygonal features),pyramids, or ellipsoids. Combinations of the different structure shapescan be utilized. The preferred shapes include those selected from thegroup consisting of hemispheres, prisms, and pyramids. Each individualstructure should typically have a height of greater than about 3micrometers but less than the total thickness of the adhesive layer, andpreferably about 3 micrometers to about 50 micrometers. Additionally,some of the structures may be truncated to provide a surface foradditional structures, to control the contact surface of the adhesives,and to improve the wet out of the adhesive. FIG.3A illustrates aquadrangle pyramid 40 as an illustration of one embodiment suitable foruse with the present invention. FIG. 3B depicts a truncated quadranglepyramid 41 that may also be embossed in the pressure sensitive adhesiveof the invention.

In the adhesive-backed article of the present invention, the regularpatterns or groups of structures have a specific shape and a size toachieve the desired performance parameters. Therefore, the structuresare arranged at a pitch (average value of a distance between similarstructural points of adjacent structures) of about 400 μm or less, andpreferably about 300 μm or less. A pitch larger than 400 μm mayundesirably result in a pattern of the features appearing on the surfaceof the film after application, thereby causing deterioration in thequality of the article's appearance.

Double featured structures are an additional embodiment that aresuitable for use in the present inventive article. The stacking or useof two structures enhances the positionability of the article by furtherreducing the initial contacting surface of the adhesive. FIG. 4Aillustrates a truncated, quadrangle pyramid 42 having an exposed surface43. A second quadrangle pyramid 44, having a base 45, is positioned onexposed surface 43. FIG. 4B depicts another embodiment highlighting thedouble features of the invention. A rectangular feature 46 provides abase 47 for receiving a base 49 of a second smaller rectangular feature48. In general, the base surface of a second structure is smaller thanthe exposed surface of the first feature. Additionally, differentconfigurations or shapes may be combined with base structures to achievethe desirable positioning properties for the present invention.

The positionability of the article is affected by the area of theadhesive that initially contacts the substrate. Preferably, the contactarea of the microstructured features results in an initial surfacecontact area of about 60% or less of the total area of the adhesive inthe plane parallel to the continuous layer of adhesive. Thepositionability of the present invention is determined by the test notedin the “Examples” section. Preferably, the article of the presentinvention exhibits a positionability test rating of 2 or better.

FIGS. 5-7 are utilized to demonstrate the various dimensions andcharacteristics of the microstructured surface of the pressure sensitiveadhesive. The figures represent idealized shapes corresponding to theliner. Those skilled in the art will recognize the pressure sensitiveadhesive cannot hold exact tolerances with the scale of the structuresutilized in the present invention. FIG. 5 is a segmented perspectiveview of a pressure sensitive adhesive used in the present invention. Theadhesive 50 has a plurality of structures 52. The pitch P between thefeatures 52 is not more than 400 μm. The height h of each feature 52from the channel 54 is within a range from 3 to 30 μm, the length W₁ ofthe upside of the channel 54 is within a range from 1 μm to the size ofthe pitch P and furthermore a length W₂ of the base of the channel 54 iswithin a range from 0 μm to the size enough to make a base angle ∠ ofthe feature to a value within a range from 1 to 90°. The aspect ratio ofthe corresponding channel would be no greater than 20.

FIG. 6 is an illustration of an adhesive 60 having a truncated structure62 with a second structure 64 positioned on an upper surface 63 of thetruncated structure 62. The pitch P measured from corresponding edges ofsecond structure 64 is not more than 400 μm. The height of eachstructure from the base of the channel 66 is in a range of about 1 μm toabout 30 μm. The length W₁ of the upside of the channel 66 is within arange from 1 μm to the size of the pitch P and furthermore a length W₂of the base of the channel 66 is within a range from 0 μm to the sizeenough to make a base angle α₁ of the structure 62 to a value within arange from 1 to 90°. A base angle α₂ of the second structure 64 iswithin a range from 1 to 90°.

FIG. 7 corresponds to the adhesive layer 70 having a microstructuredsurface 72 in the shape of a quadrangular pyramid. The pitch P betweenthe structures 72 is equal to the length W₁ of the upside of the channel74 and is not more than 400 μm. The height h of each structure 72 fromthe base of the channel 74 is within a range from 3 to 30 μm. The lengthW₂ of the base of the channel 74 is 0 μm.

The use of a release liner or backing is one method suitable for formingthe microstructured adhesive of the present invention. The release linercan be advantageously made of various materials. Preferred materialswhich the microstructured liner may include, but are not limited toplastics such as polyethylene, polypropylene, polyesters, celluloseacetate, polyvinylchloride, and polyvinylidene fluoride, as well aspaper or other substrates coated or laminated with such plastics. Theseembossable coated papers or thermoplastic films are often siliconized orotherwise treated to impart improved release characteristics. Thethickness of the release liner can vary widely according to the desiredeffect. Furthermore, it is possible to afford structures to the releaseliner by using various techniques, such as those disclosed in U.S. Pat.No. 5,650,215 (Mazurek), herein incorporated by reference in itsentirety.

Suitable release liners as well as adhesive layers on release liners arefurther described in U.S. patent application Ser. No. 09/808,636, filedon Mar. 14, 2001 by Fleming et al., herein incorporated by reference inits entirety.

FIG. 8 depicts a liner 80 suitable for creating structures on thesurface of an adhesive. The liner 80 includes protrusions 82 that formchannels in an adhesive as the adhesive is cast onto the liner.

The article of the present invention is produced by imparting theinventive microstructured surface onto an adhesive with practicesconventionally recognized in the art. The features are imparted byembossing the adhesive directly through utilization of molding tools orby coating the adhesive onto a liner or backing previously embossed withthe inventive features. Such methods and practices are fully disclosedin U.S. Pat. No. 5,650,215, previously incorporated by reference.

The above-described article can be applied to a variety of substrates,including smooth air-tight surfaces. It is important to match a specificpressure sensitive adhesive to a substrate in order to achieve thedesired level of adhesion. Examples of suitable substrates includeglass, metal, plastic, wood, and ceramic substrates, and paintedsurfaces of these substrates. Representative plastic substrates includepolyvinyl chloride, ethylene-propylene-diene monomer rubber,polyurethanes, polymethyl methacrylate, engineering thermoplastics(e.g., polyphenylene oxide, polyetheretherketone, polycarbonate), andthermoplastic elastomers. The substrates are generally smooth substratesthat accentuate the need for an article with fluid egress. Substrateswith rough surface inherently provide an egress for fluids trapped aninterface of an applied article because the rough surface permits fluidflow.

The application of the article requires the positioning of the articleover the substrate. The microstructured surface of the present inventionenable the movement of the adhesive-backed article about the surface ofthe substrate until pressure is applied to enable adhesive contact andwet out of the adhesive on the surface of the substrate. The appropriatelevel of pressure and resulting wet out will create a bond between theadhesive and the substrate.

Upon forceful application of the article, the channels permit anyentrapped fluid to bleed out around the periphery of the article,thereby eliminating air bubbles. Additionally, the microstructuredfeatures of the present invention at least partially collapse duringapplication of the article and thereby increase the amount of adhesivein contact with the substrate. The at least partial disappearance of thechannels is indicated through the wet out test, described in the“Examples” below. The present invention demonstrates wet out testresults of at least 85%, and preferably at least 95%. The at leastpartial disappearance of the channels ensures that the article has adesirable level of adhesion to the substrate.

In accordance with the present invention, the microstructured surface ofthe article is substantially undetectable from the surface of the filmand therefore improves the overall appearance of the article. One methodfor measuring the appearance involves the use of the surface roughnesstest procedure, fully described in the “Examples” section. The presentinvention, upon application of the article onto a substrate, exhibit,from the upper surface of the compliant film, an appearance having noperiodicity or repetitive pattern. Additionaly, the present inventionhas a surface roughness no greater than the roughness of the film byitself.

The invention will now be described further by way of the followingnon-limiting examples.

EXAMPLES

Surface Roughness Test

The surface topography of a film is measured using the RST Plus surfaceprofiling system available from Wyko Corporation in the verticalscanning interferometer mode (VSI) at a magnification of 1.2× and apixel size of 13.64 μm.

The system uses an interference microscope and a computer algorithm toanalyze the surface. In the system, a white light beam passes through amicroscope objective to the sample surface. A beam splitter reflectshalf of the incident beam to a reference surface. The beams from thesample and the reference surface recombine at the beam splitter to forminterference fringes which are alternating light and dark bands that arevisible when the surface is in focus. The reference arm containing theinterferometric objective moves vertically to scan the surface atvarying heights using a linearized piezoelectric transducer to controlthe motion. The interference fringes for white light are present onlyover a very shallow depth for each focus position so the fringe contrastat a single sample point reaches a peak when the point is in focus. Thesystem starts above the focus point and scans the surface at evenlyspaced intervals as the camera captures frames of interference datawhich contain interference signals for each point on the surface. Acomputer algorithm processes the data to calculate surface heights.

A single line analysis of the surface, such as those indicated in FIGS.9 and 10, provides a plot of the surface heights along a single line ofthe sample. The peaks on the plot show whether or not the surface hasany periodicity, i.e., a repeating pattern of peaks. The analyses areperformed with the tilt term removed to eliminate extraneous data due tothe interferometer configuration. The magnification is 1.2× and thepixel size is 13.64 μm. Evidence of periodicity for an adhesive backedfilm is generally apparent when the roughness of the adhesive-backedfilm exhibits a surface roughness greater than the surface roughness ofthe uncoated film. The surface roughness (Ra) is the arithmetic averageroughness for the area sampled.

Percent Wetout Test

This technique is used to study the wetting of an adhesive having amicrostructured surface onto a smooth transparent substrate. Thehardware used with this technique consists of a stereo-microscope(Olympus Model SZH-ZB), a video-camera (Cohu Model 4815) mounted on themicroscope, a coaxial vertical illuminator (Olympus Model TL2), and acomputer (Hewlett-Packard Vectra QS/20) with a video digitizing board(Imaging Technologies PCVISIONplus) installed which allows the computerto capture and digitize an image. Such an image can subsequently bestored and analyzed by commercial software packages (Jandel JAVA). Thecoaxial vertical illuminator provides light which is sent through thelens (i.e., the optic axis) to illuminate the subject. This light passesthrough a circular polarizer mounted on the end of the planar objectivelens of the microscope. In practice, the procedure is as follows:

-   1. Apply the adhesive tape onto a glass (or other optically clear    and flat) surface with one pass of a 2 kg roller.-   2. Position the laminate so that the adhesive/glass interface is    viewed through the glass by a stereo microscope.-   3. Adjust the sample so that the glass is perpendicular to the optic    axis.-   4. Adjust the circular polarizer to optimize light intensity and    contrast.-   5. Using the image analysis software, capture and digitize the    image.-   6. Set the software grey value window of acceptance to accept only    those grey values (i.e., brightness levels) corresponding to the wet    areas.-   7. Upon application of the tape, analyze the total wetted area as a    percentage of the total imaged area.    Slide Test for Positionability

A horizontal glass plate, at about 23° C., was cleaned with methyl ethylketone (MEK). A test sample (i.e., pressure sensitive adhesive on theindicated backing), approximately 2.5 cm by 7.5 cm, was draped flat ontothe glass plate with the pressure sensitive adhesive side down forapproximately 10 seconds. The end edge of the sample was lifted andpulled laterally. The test ratings are as follows:

-   1. sample slid freely-   2. sample slid easliy with some resistance-   3. sample slid with considerable resistance because of adhesion to    the plate, but could be lifted without damage-   4. sample stuck to the plate and could not be repositioned without    damge    Volume of Air Channels

The volume of the air channels were calculated based on the sizes of themicrostructures in a 500 micrometer diameter circle in the liner. Theresults are reported in cubic microns per 500 μm circle. The volume ofair channels is calculated and indicated in Table 1.

Examples 1-11 and Comparative Examples C1-C5

Embossing rolls were cut with diamond tools or laser machined to providepatterns having varying pitch, depth, widths at the top of the channeland at the base of the channel, and base angles. Polyethylene coatedpaper release liners having a silicone coating over the polyethylenes,such as those available from Rexam or Inncoat, were embossed between aheated rubber roll and each of the embossing roll to producemicrostructured liners with ridges. The rubber roll was heated to atemperature of 110° C. and the polycoated paper was heated to a surfacetemperature of 110° C. before entering the nip between the rubber rolland the embossing roll. The liners traveled around approximately half ofthe embossing roll, and then onto a cold can which cooled the liner. Thedimensions of the microstructures on the liners are shown in Table 1 andhave the shape of inverted square pyramids. The pitch is the distancefrom one microstructure to the same point on the adjacentmicrostructure, the height is the height of the microstructure from thebase of the channel, W1 is the length of the top of the trapezoidalchannel and W2 is the length of the bottom of the trapezoidal channel.

A solvent based acrylic pressure-sensitive adhesive was preparedaccording to the pressure sensitive adhesive (PSA) copolymer procedureof U.S. Pat. No. 4,737,577, incorporated herein by reference, using 90parts isooctyl acrylate and 10 parts acrylic acid. The PSA was dilutedto about 25% solids with an aziridine crosslinking agent, such as thosedisclosed in U.S. Pat. No. 5,648,425.

The pressure-sensitive adhesive solution was coated onto themicrostructured liners to a dried coating thickness of about 30micrometers. The solution on each liner was dried at 100° C. for 10minutes to form an adhesive film having a microstructured surfacedefining trapezoidal channels with the approximate dimensions calculatedfrom the liner shown in Table 1.

The exposed adhesive side of each example was then laminated at roomtemperature to a 50 micron thick primed white plasticized flexible andcompliant vinyl (PVC) film primed with an acrylic polymer modified with2-methylaziridine. The primer was an amine functional acrylic polymer inethyl acetate. The lamination was made using a two roll nip to provideflat pressure-sensitive adhesive coated PVC films. The films were testedfor Appearance, Air Bleed Capability, Slidability, and Wet-out accordingto the above described Test Methods. Test results are shown in Table 1.TABLE 1 Avg. Vol (μm³) Pitch Height W1 W2 per any 500 μm Air μm μm μm μmAngle α1° circular area Appearance Bleedability Slidability Wet-out % 1126 16 34 17 62 1.1 × 10⁶ Good Good 3 2 198 21 67 3 39 1.1 × 10⁶ GoodGood 3 90.4 3 198 22 28 3 62 6.1 × 10⁵ Good Good 3 93.5 4 197 15 18 1 602.8 × 10⁵ Good Good 3 98.4 5 200 15 200 0 9 1.9 × 10⁶ Good Good 2 98.7 6* 197 25 197 3 28 3.3 × 10⁵ Good Good 2 99.0 7 203 20 35 12 60 8.5 ×10⁵ Good Good 3 8 297 20 35 12 60 6.0 × 10⁵ Good Good 3 9 198 19 38 2272 9.9 × 10⁵ Good Good 10  198 19 28 11 71 6.3 × 10⁵ Good Good 11  19720 24 1 60 4.8 × 10⁵ Good Good 3 98.5 C1 1270 22 61 27 52 ** Poor Good 3C2 770 20 143 96 40 ** Poor Good 3 C3 508 20 35 12 60 ** Poor Good 3*Includes a secondary feature with a base angle of 60°** Volume indeterminate within a given 500 μm circleExamples 1 -11, produced in accordance with the present invention,exhibit good appearance, good air bleedability, and at least fairslidability. The appearance was determined by visual examination withthe unaided eye. A good appearance result indicates no observableunderlying structure. A poor appearance results if the pattern isvisible. With respect to Examples C1-C3, the average volume per any 500μm diameter circular area is indeterminate since some 500 μm diametercircular areas do not have channels. Additionally, Examples C1-C3 havepoor appearance indicating that patterns created by the channels arevisible with the human eye after application.

Samples from each Example measuring approximately 2.54 cm by 2.54 cmwere then laminated to a clean glass plate using a plastic squeegee. Thesamples were then analyzed for surface roughness and periodicityaccording to the procedure described above. Example C4 is the vinyl filmwith no adhesive laminated to it, and C5 is the vinyl film with anon-structured PSA laminated to it. Results are shown in Table 2. TABLE2 Ex R_(a) Value - μm Single Line Analysis PSD 1 0.99 Irregular peaks,no No spikes peridocity 2 0.50 Irregular peaks, no No spikes periodicity5 0.85 Irregular peaks, no No spikes periodicity 6 0.54 Irregular peaks,no No spikes periodicity C2 1.60 Definite repeating peaks C4 1.31Irregular peaks, no peridocity C5 0.65 Irregular peaks, no periodicity

Examples 1, 2, 5 and 6 have arithmetic average roughness valuescomparable to that of a vinyl film (Example C5). Example 2, asillustrated in FIG. 9, shows no periodicity or repeating patterns.Example C2 has a higher arithmetic average roughness, but moreimportantly a repeating pattern or periodicity as indicated by theinterferometer data. The periodicity of Example C2, as illustrated inFIG. 10, corresponds to the pitch of the channels in the structuredsurface of the adhesive. The patterns in C2 are detectable with thehuman eye. Example C4 has a roughness greater than the vinyl film(Example C5) due to microbubbles present in the adhesive. Examples C4exhibits no periodicity because the adhesive is not structured.

From the above disclosure of the general principles of the presentinvention and the preceding detailed description, those skilled in thisart will readily comprehend the various modifications to which thepresent invention is susceptible. Therefore, the scope of the inventionshould be limited only by the following claims and equivalents thereof.

1. An adhesive-backed article, comprising: a compliant polymeric film having an upper surface and a lower surface, said compliant film having an inelastic deformation of at least 5 percent after being stretched once to 115 percent of its original length; and a pressure sensitive adhesive permanently bonded to the lower surface of said compliant polymeric film, said pressure sensitive adhesive having a microstructured surface that can be bonded to a substrate, opposite said film, with a pattern of channels being formed in said surface that define a volume of at least 1×10³ μm³ per any 500 μm diameter circular area of said pattern so that, after final application of said article onto the substrate, the upper surface of said compliant film has an appearance with substantially no periodicity and substantially no surface roughness beyond the surface roughness of the film by itself in accordance with the surface roughness test procedure, wherein said channels define exit pathways that provide a fluid egress from behind said article when said article is applied to the substrate.
 2. The article according to claim 1, wherein after final application of said article onto the substrate, the pattern of said channels is prevented from appearing on the surface of said compliant film.
 3. The article according to claim 1, wherein said compliant film has a thickness of 300 μm or less.
 4. The article according to claim 1, wherein said compliant film has a thickness of about 25 μm to about 100 μm.
 5. The article according to claim 1, wherein said compliant film comprises at least one of the plastic materials from the group consisting of vinyl, polyvinyl chloride, plasticized polyvinyl chloride, polyurethane, polyethylene, polypropylene, fluororesin or the like.
 6. The article according to claim 1, wherein the average distance between adjacent channels in said pattern is up to 400 μm.
 7. The article according to claim 1, wherein said channels have an aspect ratio in the range of about 0.1 to about
 20. 8. The article according to claim 1, wherein said adhesive-backed article is sealable as indicated by an initial wet out test result of at least 85%.
 9. The article according to claim 1, wherein said channels define exit pathways that provide a fluid egress to a periphery of said article, when said article is applied to the substrate.
 10. The article according to claim 1, wherein the article is a decorative article.
 11. The article according to claim 1 in combination with a motor vehicle.
 12. A method of preparing an adhesive-backed article, said method comprising: providing a microstructured release surface and a pressure-sensitive adhesive; using the microstructured release surface to form a microstructured surface in the pressure-sensitive adhesive, where the microstructured surface can be bonded to a substrate and a pattern of channels is formed in the microstructured surface that define a volume of at least 1×10³ μm³ per any 500 μm diameter circular area of the pattern; and permanently bonding a compliant film to a surface of the pressure-sensitive adhesive that is opposite the microstructured surface, wherein channels formed in the microstructured surface of the pressure sensitive adhesive define exit pathways providing fluid egress from behind the article.
 13. The method according to claim 12, wherein said using the microstructured release surface comprises forming the microstructured surface into a layer of the pressure sensitive adhesive, and said permanently bonding comprises bonding the compliant film to a surface of the layer that is opposite the microstructured surface.
 14. The method according to claim 12, wherein the microstructured surface of the pressure-sensitive adhesive is formed by (a) coating the pressure-sensitive adhesive onto the microstructured release surface or (b) embossing the pattern into the pressure-sensitive adhesive with the microstructured release surface.
 15. The method according to claim 12, wherein the channels that define exit pathways provide fluid egress to a periphery of the article.
 16. The method according to claim 12, wherein the article is a decorative article.
 17. A method of applying an adhesive-backed article to a substrate, said method comprising: providing an adhesive-backed article comprising a pressure-sensitive adhesive layer having a microstructured surface and an opposite surface bonded to a compliant film, the microstructured surface having channels that define exit pathways providing a continuous fluid egress from behind the microstructured surface, with the channels having a volume of at least 1×10³ μm³ per any 500 μm diameter circular area of the microstructured surface and having an aspect ratio of about 0.1 to about 20; adhering the microstructured surface of the pressure-sensitive adhesive layer to the surface of a substrate, wherein after final application of said article onto the substrate, the upper surface of the compliant film has an appearance with substantially no periodicity and substantially no surface roughness beyond the surface roughness of the film by itself in accordance with the surface roughness test procedure
 18. The method according to claim 17, wherein the pressure-sensitive adhesive has an initial wet out test result of at least 85 percent, after said adhering.
 19. The method according to claim 17, wherein the substrate is part of a motor vehicle 7
 20. The method according to claim 17, wherein the article is a decorative article. 